The present invention relates to fullerenic nanostructures and a method of their production. Fullerene C.sub.60 and C.sub.70, closed-cage carbon compounds containing both six-member and five-member rings and an even number of carbon atoms, were first reported by Kroto et al. in carbon vapor produced by laser irradiation of graphite, a "carbon vaporization" technique (Nature 318 162-164 (1985)). Since then, the number of known fullerenes has rapidly expanded from C.sub.60 and C.sub.70, to include C.sub.76, C.sub.78, C.sub.84 and larger structures, including "giant fullerenes", characterized as having C.sub.n with n.gtoreq.100, nanotubes and nanoparticles.
The composition and structure of the larger fullerenic structures or "nanostructures" have generated considerable attention. Experimental evidence suggests that giant fullerenes are formed along with smaller fullerenes in carbon vaporization systems. Carbon clusters up to C.sub.632, all even numbered and interpreted to be fullerenes, were observed in molecular beam mass spectrometer (MBMS) analysis of the vapor from laser vaporization of graphite. Mass spectroscopy of solvent extracts of soot from electrical vaporization of carbon rods showed species interpreted to be C.sub.188, C.sub.208 and C.sub.266. Transmission electron microscopy (TEM) of crystals consisting largely of C.sub.60 revealed apparently ellipsoidal fullerenes estimated to be .about.C.sub.130. Scanning tunneling microscopy (STM) of extracts of soot from electrical vaporization of carbon showed spheres of 1 to 2 nm van der Waals (vdW) diameter which may correspond to fullerenes up to C.sub.330.
Multiple polyhedral shells separated by about 0.34 nm (close to the interlayer spacing of graphite) and exhibiting spheroidal, elongated and tubular shapes also have been observed by TEM. These multishelled polyhedrons were given the name "nested polyhedrons" because the innermost shell was "nested" within the polyhedral shell of larger dimension. Nested spheroidal polyhedron shells of carbon were first observed by Iijima in carbon deposited from an arc discharge at 10.sup.-7 torr (J. Phys. Chem. 91, 3466-7 (1987)). The central shells ranged from .about.1 nm diameter to much larger, some containing one- and two-layered giant fullerenes equivalent to .about.C.sub.3700 and larger. Subsequently, strikingly spherical onion structures with up to .about.70 shells were produced by intense electron-beam irradiation of carbon soot collected from an arc-discharge apparatus. Nested spheres and polyhedral spheroids 5-20 nm in diameter and other polyhedrons of approximately triangular, tetragonal, pentagonal and hexagonal cross section have also been observed. Nanostructures formed on the cathode during arc-discharge carbon vaporization include tubes with 2 to about 50 nested shells. The tubes are capped by polyhedral domes, sometimes having conical transitions to the cylindrical tube wall. All of these nanostructures contain the feature associated with fullerenes of a structure containing both six-member and five-member carbon rings.
Carbon vaporization processes, while capable of making a wide variety of fullerenic structures, are very inefficient and not amenable to large scale production. It is desirable to develop a manufacturing process that is efficient and capable of processing large amounts of fullerenic nanostructures.
Fullerenes C.sub.60 and C.sub.70 have been successfully synthesized and collected in flames by Howard et al. (Nature 352, 139-141 (11 Jul. 1991)). Evidence of high molecular weight ionic species consistent with an interpretation as being fullerenic structures was observed in low-pressure premixed benzene and acetylene flames (Baum et al., Ber. Bunsenges. Phys. Chem. 96, 841-857 (1992)). The presence of neutral giant fullerene molecules in flames has not been established, however.
It is an object of the invention to provide a method for synthesizing fullerenic nanostructures in flames. It is a further object to provide a method for synthesizing fullerenic nanostructures having both ends of the nanostructure capped. It is yet a further object of the invention to describe a method for production of soot having a high fullerenic carbon content.